HIV treats genetic disease

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For a long time HIV has been associated with incurable illness, but it could be the answer to solving some genetic disorders.

Using the outer coat of the virus as a form of molecular packaging known as a "vector", healthy copies of a gene called ARSA have been administered to three children with a lethal condition called metachromic leukodystrophy (MLD).

This genetic disease is usually fatal by the age of six. The defective ARSA gene carried by sufferers causes progressive destruction of structures in the brain called myelin sheaths, which insulate and support nerve cells.

The condition usually kicks in from 15 months of age and, as the disease progresses, patients experience increasing difficulties with walking, deteriorating vision and even sitting up without support is a struggle; But, since receiving a healthy version of the ARSA gene, the children in the trial have shown no progression of their MLD.

Where does HIV come in?

When HIV infects a cell it inserts its own genetic material into the host's DNA. From there, the infected cell begins to manufacture the components which make up HIV.

This characteristic is what the team at the San Raffaele-Telethon Institute for Gene Therapy (TIGET), based in Milan, Italy have taken advantage of in a paper published in Science this week.

HIV resembles a miniature football, with the genetic code of the virus sitting inside.

What the TIGET team have done is to empty the virus of its own genetic material and replace it with a healthy copy of the ARSA gene. This ARSA-loaded, modified HIV is then mixed with stem cells from the child's bone marrow, which the virus infects, inserting the new DNA.

The now-modified bone marrow cells are then re-infused into the child where they home-back to the bone marrow and begin pumping out the ARSA gene product, helping to remedy the condition.

Although this work is promising, it is not a silver bullet to eradicate genetic disease. There are still problems: often the take-up of the new genetic code by the target cells is low, and there can be mistakes when it's incorporated into the host cell genome. Previous trials using related strategies have also had difficulties with the new DNA sequences being inserted near genes called oncogenes, which regulate the growth of cells and can lead to cancer. This has caused several participants in previous trials to develop leukemia.

However, Eugenio Montini, who was involved with the study said, "Until now we have never seen a way to engineer stem cells using gene therapy that is as effective and safe as this one. These results pave the way for new therapies for other more common diseases..."